Modeling and Analysis of Magnetic Noise Characteristics of Permalloy–Nanocrystalline Magnetic Shielding Devices

Magnetic field interference poses a significant challenge to the efficient operation of ultrahigh-sensitivity ultraweak magnetic field measurements. Especially in magnetoencephalography (MEG), there is an urgent need for high-performance, low-noise magnetic shielding devices. To further suppress the magnetic noise and improve the sensitivity of MEG measurement, this article proposes the permalloy and Permalloy + Nanocrystalline (P–N) magnetic shielding box. A magnetic noise calculation model based on fluctuation–dissipation theory is proposed to predict magnetic noise accurately. The imaginary part permeability due to hysteresis losses at different frequencies and flux densities is accurately calculated using the Bertotti model, and the change of magnetic field strength due to induced eddy currents is considered, which improves the accuracy of the magnetic noise calculation. To verify the validity of the magnetic noise model, the magnetic noise calculation and experimental validation are carried out for the permalloy magnetic shielding box and P–N magnetic shielding box, respectively. The results show that the magnetic noise of the P–N structure magnetic shielding box is reduced by 34.4% compared to the permalloy structure. In the frequency range of 3–100 Hz, the average magnetic noise errors of the calculated and measured values for the two magnetic shielding structures are 7.7% and 6.8%, respectively. This study advances magnetic shielding technology for ultrahigh-sensitivity atomic sensors, enhancing their overall performance and precision.